This is a natural history study of the gastrointestinal disease that affects a subset of CVID patients. Subjects with documented weight loss or diarrhea will be compared with CVID patients without gastrointestinal symptoms; subjects will have upper and lower endoscopy to evaluate histology and obtain specimens for LPMC purification; LPMC and PBMC will be immunophenotyped and tested for cytokine secretion; intestinal absorption will be measured; spleen size will be determined. We plan to recruit up to 20 subjects. The goal is to understand the T cell abnormality contributing to the idiopathic inflammatory bowel disease that can afflict these patients. Specific patterns of cytokine abnormalities should suggest specific therapies to test in this condition.